Casting silver coins

Jewelry Discussion
1

Newbe Question here. Lost wax investment casting silver, casting 1"
size coins at the end of a tree. Tried every tree shape and angle but
the coin areas will not fill completely. Tried every angle and
tempuratres possible. Any suggestions ? Should I be useing the
centrifuedge?

2

You should try adding a sprue on the back edge of the coins to allow
for the escape of gases and complete the fill. Give that a try.

Russ Hyder
The Jewelry CAD Institute

3 
Tried every tree shape and angle but the coin areas will not fill
completely. Tried every angle and tempuratres possible. Any
suggestions ? Should I be useing the centrifuedge?

A centrifuge will indeed fill better. But first, simply try larger
diameter sprues. Incomplete fill may be because your sprues are too
small. As far as temperatures, try a higher temperature for the flask
(mold) first, and then slightly raise the pouring temperature of the
metal too if that doesn’t work.

Peter

4

Hi Maybelle

It’s hard to judge without actually seeing the piece.

The place where you may have a problem is in your sprueing —
either too thin or not enough. When I’m doing a piece around 25mm
diameter I typically have 3 or 4 sprues coming back to the main
sprue. These sprues should be at least as thick as piece you are
casting. With a round piece and three sprues attach them to the rim
around 120 degrees apart with one more or less directly above the
sprue base. Remember the molten metal doesn’t like to flow backwards
so visualise the flow of metal when you arrange the sprueing pattern.
It’s better to have too many sprues than not enough. They might be a
right royal pain cut off and finish back but is better than losing a
day from a spoilt casting.

Other problems may include the either the metal or the flask is not
hot enough. The metal should fluid and free running and the flask
450 C